Automatic polishing device for metallographic specimens



May 23, 1961 w. c. cooNs Erm. 2,984,951

AUTOMATIC POLISHING DEVICE FOR METALLOGRAPHIC SPECIMENS v Filed oct. 1e, 195s l l WILLIAM w. MCKIMM i 37 DAvlD w. PEASE BY Z 39) 38 R Gl/v/T United States Patent C) AUTOMATIC PULISHING DEVICE FOR METALLOGRAPHIC SPECIIVIENS William vC. Coons, Philipsburg, William W. McKimrn,

Driftwood, and David W. Pease, Snow Shoe, Pa., assignors to 'Curtiss-Wright Corporation, a corporation of Delaware Filed Oct. 16, 1958, Ser. No. 767,711

Claims. (Cl. 51-131) This invention relates to apparatus for polishing metallographic specimens, and more particularly to an inexpensive device for automatically polishing a plurality of specimens simultaneously. The present invention may be used by less skilled personnel than the previous devices, with better results and fewer dithculties.

In the prior art, metallographic specimens are polished automatically las follows. Metal specimens in the form of fragments, bars, cylinders, or other shapes are imbedded in one end of a cylindrical Bakelite mount. A number of such mounts are -then positioned in a radial holder by means of set screws, and ythe holder is fitted to a drive shaft over a horizontally rotating Wheel covered with a polishing cloth and supplied with abrasive compound. Spring pressure is applied to the drive post of the holder to provide rm contact of the specimens with the polishing wheel, and the holder is rotated in a direction oppo- Vsite to the rotation of the wheel.

There are grave disadvantages of this apparatus. It is very diiicult to secure each sample by an individual set screw and still maintain all sample surfaces in the same plane. Also, if only one sample is to be polished dummy mounts rmust be installed in the remaining apertures of the holder in order to insure even pressure; installing the dummies is time-consuming. Polishing abrasives are expensive, and since the periphery of the wheel is open the abrasive is continually being thrown off by centrifugal force into a catch basin and -thus wasted. Since several stages of polishing are usually required on metallographic specimens, several expensive wheels are required to do a complete job, as it would not be practical to strip the polishing cloth loaded with one grade of grit from a single wheel and replace it with another cloth. The specimen holder is therefore transferred successively from one wheel to another, and since the holder is of complex construction considerable cleaning time is required between steps, in order not to carry over coarse grit to the next wheel. Finally, if it is desired to inspect a specimen to determine how far polishing has progressed, the specimen must be removed from the holder for inspection, and the whole job of repositioning a set of specimens in Va holder with all faces in a single plane must be repeated before polishing can proceed.

It is therefore an object of this invention to provide an automatic polishing apparatus for simultaneous polishing of a plurality of metallographic specimens, in which the specimens are `self-aligning.

It is another object to provide an automatic polishing apparatus in which a single specimen may be polished without the use of dummy mounts.

A further object of the invention is the provision of automatic polishing apparatus which does not waste abrasive material.

Yet another object is to provide polishing apparatus by means of which a single wheel may be used for successive operations with grits of different grades.

4It is a still further object of this invention to provide F'ice automatic polishing apparatus in which the specimen mounts may be easily cleaned.

Another object is the provision of polishing apparatus which a specimen may be removed without disturbing other specimens.

A yet further object of the invention is the provision of polishing apparatus having an inexpensive and easily removable polishing dish which may be easily cleaned or discarded in the event of any contamination.

Other objects and advantages of the invention will become apparent on reading the following specification in connection with the accompanying drawings, in which Figure l is an elevation in cross-section of the apparatus of the invention, positioned for use with a s-tandard polishing wheel;

Figure 2 is a plan view of the apparatus, with mounted specimens in position for polishing; and

Figure 3 is 'a cross-sectional elevation of a rotatable dop holding a mounted specimen.

Referring more particularly to the drawings, there is shown a polishing Wheel 11 res-ting on the tapered drive shaft 12 and enclosed by the catch basin 13. These items are not ya part of the present invention, but are standard equipment with which the apparatus of the invention is designed to be used to provide la complete automatic polishing combination.

Mounted on the wheel in a driven relation thereto is the polishing dish 14 of this invention. The dish has a recessed bottom which tits snugly over the wheel, and it may be retained thereon by clamping plates 16 and bolts 17 as shown, or by any other convenient means, such as a push t with the wheel, or set screws. The dish is provided with an outer annular polishing chamber 18 formed by outer Wall 19 and inner wall 21, and a circular inner polishing chamber 22 within the inner wall. Although two such polishing chambers are here shown, the dish may be provided with a greater number, or with only one, and may be made of a size to be used with any of the various sized wheels available. Polishing cloth 23 is xed to the lloor of each chamber by any suitable adhesive 24. It is necessary that the viioors of the chambers be substantially plane, since it is these surfaces which govern the -atness of the polishing cloth. Dish 14 is preferably made of plastic for light weight, easy handling, yand low cost, but it may equally well be made of any other desired material, such as metal, glass, porcelain, etc.

A retainer ring 26 having a support flange 27 rests on the rim of the catch basin. The retainer ring is preferably formed of metal, but may be of porcelain or any other substance having suicient weight to hold it in position, as shown. If it should be desired to make the ring of plastic or other lightweight material, it may be fastened to the catch basin by clamps, set screws, or any suitable means. The inner diameter of the ring must be of suicient size to surround the polishing dish with easy clearance. The upper edge of the ring is notched 28 in four places at 90 to receive the ends of cross-bars 29 and 31, the cross-bars being provided with a lap-joint at the center so that they shall lie in the same plane. The bars may be united at the center by welding, soldering, or brazing, or the joint may simply be left loose; they thus form a four-armed spider, but it will 'be understood that a single bar may be used, or a spider having three arms or more than four, as desired.

A plurality of bearings 32 extend from the lower side of the spider arms, mounted on shouldered screws 33 as shown, or on pins or other convenient means. The bearings are so positioned that each arm of the spider has one bearing extending into each of the polishing chambers 18 and 22, making a total of eight lbearings in the pictured embodiment.

If desired, the bearings may be borne on arms or supports extending inward from the ring or from the catch basin, and the word spider as herein used is intended to cover any such restraining means.

There is provided a plurality of rotatable dops 34, best shown in Figure 3. The dops are of generally cylindrical form, and it has been found convenient in practice for them to have a flange B6 at the bottom against which rotatory force may be applied, but the ange may be omitted. Each dop contains an axial cup or recess 37 in its bottom face, adapted to receive a specimen mount 3S bearing the metallographic specimen 39 to be polished. The blind end or inner face of recess 37 is made substantially normal to the axis, in order that the dop should not rock in operation. The specimen is here shown as cylindrical, but may be of any other shape, as is well known in the metallographic art. The dops may be of more or less height, according to the amount of weight desired, and are preferably made of metal, but may also be of plastic, porcelain, or other material, by the use of which an additional variation in Weight may be achieved.

fIn the operation of the automatic polishing device, the specimen is iirst embedded in a plastic or Bakelite mount, according to standard practice. The mount is inserted into the recess in Ithe dop, with the face bearing the specimen protruding slightly therefrom; the mount may be retained in place by friction, or by cementing or by set screws. The polishing chambers are supplied with the desired grit, and any number of dops from one up to the capacity of the machine are placed into the chambers with the specimens in contact With the polishing cloth bearing the grit. The wheel bearing the dish is set in motion; centrifugal force thrusts the dops into contact with walls 19 and 21, the rotary motion meanwhile holding the leading dop against the bearing on the spider arm, which rtrains it from traveling with the Wheel. Rotary motion is imparted to the leading dop by friction between it and the outer wall of the chamber. If a plurality of dops is used in a single quadrant, the second dop will turn in a direction opposite to that of the first,

since the coeicient of friction between the metal of the two dops is greater than that between the metal and the plastic wall. Even if the dish is made of the same material as the dops, the use of a third dop in the series will insure that the second will rotate, since it will be driven at two points by the end dops, and opposed by the wall at only one point. The rotation of the dops is herein referred to as secondary rotation, to distinguish it from the rotation of the polishing wheel and the dish.

By the use of a dish with a plurality of polishing chambers, it will be seen that more than one stage of polishing may be done simultaneously on a single wheel. Although the rotational speed is ordinarily not so high as to rthrow any polishing compound over the dividing walls of the chambers, the possibility of spoiling a specimen may be guarded against by using the coarsest grit in the outside chamber, with successively liner ones inside. lt will also be apparent that many grades of polishing may be done by the use of several dishes with a single wheel, the dishes being easily interchangeable. Further, a single specimen may be removed for inspection without halting the operation on the remainder, and since there is no intricately shaped specimen holder which might 'oe irnperfectly cleaned, there is no danger of carrying a coarse grit over into the next stage.

Although the foregoing description relates to a pre- Y ferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended to cover all such modification in the appended claims.

What is claimed is: 1. In an automatic polishing device having a horizon- 4 Y tally rotatable wheel, the combination with said wheel of a polishing dish mounted thereon and rotatable therewith and having at least one polishing chamber having a circular outer wall, a polishing cloth mounted on the oor of said chamber, at least one generally cylindrical dop adapted to receive a metallographic specimen positioned on said polishing colth within said chamber with the cylindrical surface of said dop in frictionally driven contact with said circular Wall, said dop being thereby adapted to have secondary rotation imparted to it by said wall, and means for restraining said dop from traveling with Said dish.

2. In an automatic polishing device having a horizontally rotatable wheel, the combination with said wheel of a polishing dish mounted thereon and rotatable therewith and having a plurality of concentric polishing chambers, each of said chambers having a circular outer wall, a polishing cloth mounted on the iloor of each of said chambers, a plurality of generally cylindrical dops adapted to receive metallographic specimens positioned on said polishing cloths within said chambers with the cylindrical surface of each of said dops in frictionally driven contact with one of said circular walls, said dops being thereby adapted to have secondary rotation imparted to them by said walls, and means for restraining said dops from traveling with said rotary dish.

3. An automatic polishing device comprising in cornbination a horizontally rotatable wheel, a polishing dish positioned on said wheel and rotatable therewith, said dish having at least one polishing chamber having a circular outer wall, a polishing cloth mounted on the floor of said chamber, at least one generally cylindrical dop adapted to receive a metallographic specimen positioned on said polishing cloth within said chamber with the cylindrical surface of said dop in frictionally driven contact with said circular wall, said dop being thereby adapted to have secondary rotation imparted to it by said wall, a ring surrounding said dish, and restraining means mounted on said ring and extending into said chamber and adapted to restrain said dop from traveling with said rotary dish. Y

4. An automatic polishing device comprising in combination a horizontally rotatable wheel, a polishing dish positioned on said wheel and rotatable therewith, said dish having a plurality of concentric polishing chambers, each of said chambers having a circular outer wall, a polishing cloth mounted on the floor of each of said chambers, a plurality of generally cylindrical dops adapted to receive metallographic specimens positioned on said cloth within said chambers with the cylindrical surface of each of said dops in frictionally driven contact with one of said circular Walls, said dops being thereby adapted to have secondary rotation imparted to them by said Walls, a ring surrounding said dish, and restraining means mounted on said ring and extending into said chambers and adapted to restrain said dops from traveling with said rotary dish.

5. An automatic polishing device comprising in combination a horizontally rotatable wheel, a polishing dish positioned on said wheel and rotatable therewith, said dish having at least one polishing chamber having a circular outer wall, a polishing cloth mountedv on the iloor of said chamber, a ring surrounding said dish, restrainer means mounted on said ring and extending over said dish, at least one horizontally rotatable bearing mounted on said restrainer means and extending into said polishing chamber, and at least one generally cylindrical dop adapted to receive a metallographic specimen positioned on said polishing cloth within said chamber with the cylindrical surface of said dop in frictionally driven contact with said circular wall, said dop being thereby adapted to have secondary rotation imparted to it by said wall, said dop being also in rotatable contact with said bearing and being restrained thereby from traveling with said dish.

6. An automatic polishing device comprising in combination a horizontally rotatable wheel, a polishing dish positioned on said wheel and rotatable therewith, said dish having a plurality of concentric polishing chambers, each of said chambers having a circular outer wall, a polishing cloth mounted on the oor of each of said chambers, a ring surrounding said dish, restrainer means mounted on said ring and extending over said dish, at least one horizontally rotatable bearing extending into each of said chambers and mounted on said restrainer means, at least one generally cylindrical dop adapted to receive a metallographic specimen positioned within each of said chambers on said polishing cloth with the cylindrical surface of each of said dops in frctionally driven contact with one of said circular walls, said dops being thereby adapted to have secondary rotation imparted to them by said walls, each of said dops being also in rotatable contact with one of said bearings and being restrained thereby from traveling with said dish.

7. A polishing dish for an automatic polishing device, comprising in combination a bottom section having a substantially plane upper surface and a plurality of concentric vertical circular walls extending upward from said plane surface and defining therewith a plurality of polishing chambers, a polishing cloth mounted on said plane surface within each of said chambers, the lower surface of said dish having a recess therein adapted to receive a polishing wheel.

8. A polishing dish as recited in claim 1, wherein said dish is formed of plastic.

9. A polishing dish as recited in claim 7, wherein said dish is formed of porcelain.

10. A polishing dish as recited in claim 7, wherein said dish is formed of metal.

References Cited in the tile of this patent UNITED STATES PATENTS Stainbrook Dec. 2, 1941 

